1. Field of the Invention
The present invention relates to a dispensing gun, and more particularly to a dispensing gun for dispensing viscous materials, such as thick liquid, pasty materials, or mastic caulking materials.
2. Description of the Prior Art
Various kinds of typical dispensing guns have been developed for dispensing viscous materials, such as thick liquid, pasty materials, or mastic caulking materials which are normally retained in a cartridge having a discharge nozzle, and having an open end, and a cup-shaped piston slidably received in the cartridge.
One of the typical dispensing guns is disclosed in U.S. Pat. No. 5,217,213 to Lii, and comprises a rod slidably received in a disc and including a rack formed or provided therein, and a pair of pawls biased to engage with the rack for allowing the rod to be moved forward step by step, and in order to force the cup-shaped piston forward and thus to force the viscous materials out of the cartridge. The pawls may be used for forcing or pushing the rod forward step by step only, such that the viscous materials may be pressurized by the piston, and may be caused to move out of the cartridge continuously. Much of the viscous materials may thus be forced out of the cartridge, and may be wasted.
U.S. Pat. No. 5,156,305 to Eyre discloses another dispensing gun including a rod slidably received in a stock, a catch or an actuating plate engaged on the rod for moving the rod forward step by step with a trigger, a release plate engaged onto the rod, and a bush engaged with the rod and the release plate for moving the rod backward after the rod is moved or forced forward by the actuating plate, in order to release the pressure of the viscous materials, so as to prevent the viscous materials from being continuously moved or forced outward of the cartridge.
However, when the rod is moved rearward or backward by the release plate, a hollow space may be formed in the front end of the cartridge, such that, next time, when the rod is forced forward by the actuating plate again, the piston may not move or force any viscous materials out of the cartridge, until the air in the hollow space formed in the front end of the cartridge is forced out of the cartridge, or until the viscous materials are pressurized again by the piston. The actuating plate is thus required to be actuated many times, in order to force the required amount of mastic caulking materials out of the cartridge.
In addition, when the hollow space is formed in the front end of the cartridge and when the rod is moved rearward or backward by the release plate, the air may be drawn into the cartridge, such that the mastic caulking materials may be easily hardened by the air. Furthermore, when the dispensing gun is directed upward or downward, the bush may not suitably engage with the release plate, and the rod thus may not be actuated or moved rearward by the release plate, such that the viscous materials may still be caused to move out of the cartridge continuously.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional dispensing guns.
The primary objective of the present invention is to provide a dispensing gun including a pressure relieving device for relieving the pressure of the viscous materials or the mastic caulking materials, and for preventing the viscous materials or the mastic caulking materials from moving out of the cartridge continuously.
The other objective of the present invention is to provide a dispensing gun including a pressure relieving device for preventing the air from moving into the cartridge and for preventing the viscous materials or the mastic caulking materials from being hardened by the air.
In accordance with one aspect of the invention, there is provided a dispensing gun for dispensing a viscous material received in a cartridge, the cartridge including a piston slidably received therein for moving the viscous material out of the cartridge, the dispensing gun comprising a stock including a handle and at least one guide orifice, and including a frame for holding the cartridge therein, a rod slidably engaged through the guide orifice of the stock, and including a first end having a plunger provided thereon for engaging with the piston of the cartridge, means for moving the rod forwardly and rearwardly relative to the stock to force the viscous material out of the cartridge, means for limiting a rearward movement of the rod relative to the stock, and means for retrieving the rod forwardly to force the plunger to engage with the piston of the cartridge.
The limiting means includes an abutment extended from the stock, and a release plate having a hole for loosely receiving the rod. The release plate is engaged with the abutment of the stock to limit the rearward movement of the rod relative to the stock when the release plate is moved rearwardly by the rod.
A device may be provided for biasing the release plate to engage with the abutment of the stock, and/or for tilting the release plate relative to the rod.
The retrieving means includes a spring member having a first portion engaged with the abutment, and having a second portion engaged with the release plate, to bias the release plate away from the abutment of the stock. The second portion of the spring member includes at least one leg engaged through and hooked with the release plate.
The moving means includes an actuating plate having an aperture formed therein for receiving the rod, a trigger pivotally secured to the stock and having an actuating pin for engaging with the actuating plate, and means for biasing the actuating plate to engage with the actuating pin of the trigger.